1. Field of the Disclosure
The present disclosure relates to a light guide plate, which improves a hot spot phenomenon, and a liquid crystal display apparatus using the same.
2. Discussion of the Related Art
Liquid crystal display apparatus, using a liquid crystal panel as a display, are employed for handheld computers such as a laptop computer, office automation equipment, audio/video devices, indoor/outdoor advertisement display devices, and the like. A transmission type liquid crystal display apparatus, which is the most common liquid crystal display apparatus, displays an image by modulating a light incident from a backlight unit by controlling an electric field applied to a liquid crystal layer.
The backlight unit is divided into a direct type backlight unit and an edge type backlight unit. The edge type backlight unit has a structure that light sources are disposed to face a side of a light guide plate and a plurality of optical sheets are disposed between a liquid crystal panel and the light guide plate. In the edge type backlight unit, the light sources irradiate light to one side of the light guide plate and the light guide plate converts a linear light source or point light source into a surface light source. The direct type backlight unit has a structure in which a plurality of light sources are disposed under the liquid crystal display panel and irradiate light diffused through a diffusion plate to the liquid crystal panel.
Of the two, the edge type backlight unit has the problem of the hot spot phenomenon because light is supplied to a side of the light guide plate.
FIG. 1 is a view for explaining the hot spot problem, which is a top plan view selectively showing light emitting diodes LED1 and LED2 used as light sources and a light guide plate 10.
As illustrated in FIG. 1, the first and second light emitting diodes LED1 and LED2 are disposed at an one side so as to face an edge of the light guide plate 10. As is generally known, the light emitting diodes are directional elements, and a light thus enters the light guide plate 10 at a predetermined directivity angle (α). As such, there exists a portion (a slashed portion in the drawing, hereinafter, “shaded area GA”) where light coming from the first light emitting diode LED1 and light coming from the second light emitting diode LED2 are not mixed up together. Accordingly, the shaded area GA looks dark, and a portion where a light comes from the first light emitting diode LED1 and the second light emitting diode LED2 (hereinafter, “emission area WA”) looks bright, which generates a difference in brightness depending on position and leads to the hot spot problem. FIG. 2 shows an actual appearance of a liquid crystal panel where the hot spot phenomenon occurs. In FIG. 2, it can be seen that an incident plane of the light guide plate 10 facing the light emitting diodes has a wave-like pattern due to the hot spot (inside the box in FIG. 2). If light appears to be wave-like, the luminance of the liquid crystal panel becomes non-uniform due to the wave-like pattern of the light guide plate, because the light guide plate is a component that changes a point light source into a surface light source and supplies light to the liquid crystal panel disposed above it, thus failing to properly display an image in a desired shape.
A simple way of overcoming this hot spot problem is to increase the number of light emitting diodes. That is, the hot spot problem can be overcome by arranging light emitting diodes densely enough to prevent the formation of the shaded area GA illustrated in FIG. 1. However, such an increase in the number of light emitting diodes requires higher power consumption, which is not desirable.
Another way is to increase bezel size so that a hot spot portion is blocked and not visible. The liquid crystal panel and the backlight unit are normally packaged in a case: a back cover and a front cover are coupled together to package the liquid crystal panel and the backlight unit interposed therebetween. Being packaged, the edges of the liquid crystal panel are blocked by the front cover. The portion at which the liquid crystal panel is blocked by the front cover is referred to as a bezel. The bezel covers the liquid crystal panel on the front side, thus reducing the size of the display area where the liquid crystal panel displays an image.
Recently released liquid crystal display apparatuses are reduced in bezel size and thus have an enlarged display area, which appeals to consumers in terms of design. As such, the method of increasing bezel size for the purpose of solving the hot spot problem is not advantageous because of a reduction in display area, and is undesirable in terms of design.